Process for forming nitrogen oxides



Aug. 25, 1959 J. F. HALLER PROCESS FOR FORMING NITROGEN OXIDES FiledAug. 18, 1955 INVENTOR.

John F.Hol1er BY WWI/9&

ATTORNEYS United States Patent PROCESS FOR FORMING NITROGEN OXIDES JohnHaller, Mount Carmel, Conn., assignor to Olin Mathieson ChemicalCorporation, a corporation of Virginia Application August 18, 1955,Serial No. 529,234

9 Claims. (Cl. 23163) My invention relates to the novel application ofdetonation or shock waves to bring about chemical reactions.

I have found that passing a detonation or shock wave through a gaseousmixture comprising nitrogen and oxygen produces nitrogen oxides.According to my invention, a make charge of a gaseousmixture comprisingnitrogen and oxygen is introduced into a portion of a reaction space anda detonatable material is introduced into the remaining portion. Thedetonatable material is detonated and the detonation Wave impinges onthe make charge causing reaction between the nitrogen and oxygen andformation of nitrogen oxides. The nitrogen oxides produced are suitablefor use in making the corresponding acids.

The detonatable or explosive material can be any which is adaptable todetonation by spark or other suitable ignition means to produce adetonation or shock wave. It is advantageous to choose one which iscompatible with the reactants and products of the reacting section. Theuse of a mixture of hydrogen and oxygen in this invention isparticularly advantageous as the water formed in the explosive reactionis utilized for the hydrolysis of the nitrogen oxides, while any excessis easily condensed from unreacted nitrogen and oxygen thus permittingtheir efficient recycling. Other suitable explosive mixtures such asethylene and oxygen or acetylene and oxygen can be used. The reactantsare used in stoichiometric amounts. Air can be used instead of oxygen.Explosive substances such as chlorine dioxide or hydrazoic acid can alsobe used. The make charge consists of a gaseous mixture comprisingnitrogen and oxygen.

My invention will be further illustrated by reference to theaccompanying drawing which is a diagrammatic drawing of one suitableform of apparatus for conducting the process of the invention.

The reaction chamber 1 is a nickel pipe, e.g. a pipe seven feet inlength and one inch in diameter. The reactor can be operated underelevated or reduced pressure. Elevated or reduced pressures areadvantageous depending on Le Chateliers principle of volume change. Thuswhere the volume of the reactants is greater than that of the products,the use of elevated pressures is advantageous. Increased pressures alsoincrease equipment capacity and permit the use of more intensedetonation waves. Approximately the upper three feet of the reactor tubeare filled with, for example, hydrogen and oxygen gas in a ratio ofabout 2:1, while the remaining lower portion is filled with nitrogen andoxygen gas in a 1:1 ratio. The lower' portion is filled through inlets 2and 3. The gases pass through gas mixer 4 and through the coiled coppertubing 6 which protects the rest of the apparatus from the effect of thedetonation wave. The sidearm of mixer 4 has a flexible connection tocoil 6. The filling of the upper portion of the tube is done throughinlets 7 and 8 and is controlled by the electric hosecock 9. Both tubes7 and 8 pass through hosecock 9 and both tubes are closed icesimultaneously by the operation of the bar of the hosecock. The purposeof the hosecock is to cause intermittent flow of the explosive gases andthus prevent their continuous burning. The product is emitted from theexit tube 10, fitted with an electrically controlled stopcock 11.

The operation of the ignition by the spark plug 12, the electricalhosecock 9, and the stopcock 11 is automatically controlled by means ofthe electrical circuit 13. The timing is controlled by a series ofrelays, the central relay consisting essentially of a small synchronousmotor whose rotating axle makes and breaks the circuit.

The reactor suitable for use in the process is of a size suitable toproduce a detonation wave. For example, Laffite et al., Compt. rend.183, 283 (1926), have shown that an oxygen-hydrogen explosion musttravel for at least 70 cm. in a tube of at least one inch in diameterbefore a shock wave is produced. The size of the reactor can vary over aconsiderable range. The reaction is carried out in a confined reactionspace as, for example, the reactor of the drawing which is a closedtube. By the term confined I mean to include, however, reactors whichare open at the end opposite the explosion end. The explosion end of thetube must be closed but the opposite end of the reactor can be open orclosed. Advantageously, the tube can open into a larger volume where thegaseous products are collected. Preferably, the reaction space iselongated.

Certain modifications of the reactor can be advantageous for dilferentreactions. For example, the reaction portion, i.e. the nitrogen-oxygenreaction portion, of the tube of the drawing need not be cylindrical,but can taper to an appropriately smaller diameter, or it can widen, inwhich case the whole tube assumes a funnel shape. The former variationis valuable when carrying out an endothermic reaction, which wouldconsume the energy of the shock wave at a greater rate than usual. Thetapering permits the wave to pass through the entire length of thereactants with undiminished intensity. Conversely, an exothermicreaction would increase the intensity of the wave. In this case thereaction section of the tube can funnel out, thus nullifying anyincrease in intensity and permitting the use of a larger volume ofreactants. The length of this section should be as long as possible toobtain good yields, but is limited by the distance through which theshock wave will travel substantially undiminished in the specificreactants used.

The reactor is preferably positioned vertically with that end at the topwhich contains the less dense gas mixture but the reaction portion canbe extended horizontally. This tends to prevent mixing of the reactingand exploding components.

The detonation charge and make charge can be separated in the reactor bya separating medium such as, for example, a rupturable diaphragm, e.g. acellophane diaphragm, or a narrow zone of inert gas. The separationprovides more certain ignition of the detonation charge as it insuresits uncontamination and thus provides closer control over the process.The separation medium is particularly useful when the detonation chargeand make charge are not compatible. Although it is preferable to usecompatible gas mixtures, thus avoiding the use of a diaphragm betweenthe detonation charge and the make charge, such a diaphragm can be usedpro vided it is of exceedingly low inertia so as not to decrease theshock intensity. An important advantage of a diaphragm is to preventdiffusion of the reaction gases into the detonation gases withconsequent loss of wave intensity. A soap bubble film, for example, canbe used as a diaphragm.

The mechanism of the process is not clearly understood; ut -the reactionadiabatic heating and cooling which is produced by the shock Wave.

is probably-"due to the rapid Myinvention willebe further illustratedb ythe follow ing'ex-amples conducted with the apparatus of the drawing. vI z ;..E mp.

The gas flow and the electrical circuit was arranged so thattheigasesfilled the tube in 54 seconds. This re-- quired-310 cc. of-H and-155cc.- of- O in the'upper section of the'tube, and 309cc. of leach O and Nin theolowerpotrion of i the tube.--The= electrical hoseco'ck thenstoppedthe flow of H and O'g'forsix-seonds and thekexplosio'nwasproduced.--- The gases formed -Were' led into 25 cc. of Water with apH of 5.50. Afterex plosi'o'nstook place (over aperiodof "20 minutes)-"the pH.-of-1 the-'-water dropped to 3-;20.- This Was due to theformation of nitric acid in water.

Exzrntp le Since water was being continuously condensed on the innerwall of tube during its operation, a portion" of the nitrogen oxides wasdissolved therein. This did' not have-s'uflicienttime to drain (as wouldbe the casein an applied, eontinuous operation of-this apparatus) duringthe short-runs-of these experiments. -'To determine the amount of acidretainedin the tube, it wasflushed with" water; after a run of 3detonations.- This'rinse: 'Water Wasad ded to the waterin which theeffluent gases'were collected-.--A tot-a1 of-1340 cc. of 'water was"collected." j The original pH of the waterwas 5.15,. Thecombined;

sentially of nitrogen and oxygen, confining in anotheri portion of thereaction space a detonation charge of a material which will detonate"upon"ignition; igniting 'tli' detonation charge, impinging theresulting detonation wave against the make charge whereby the nitrogenand oxygen of the make charge are caused to react.

2. The process of claim 1 in which the material which will detonate onignition is a mixture of oxygen and hydrogen. v

3. The process of claim 1 in which the reaction space is an elongatedreaction space. we: w n

4;. The process:ofJ-claimr 1 in=whihc the reaction space is a confinedelongated reaction space.

5. Theprocess of claim 1 in which the reaction space isaclosedtube. i AN 6. The process O'fitclairr'i ilin which a separating medium isinterposed between the make charge and detonation charge.

7. The process of claim 1, the proportion of nitrogen and oxygen presentin the make charge being such as to cause combination of nitrogen andoxygen to form said nitrogen oxides.

8. The process ofclaim 1 wherein nitrogen and oxyi gen present in themake charge are in about stoichiometric amounts.

The process of claim-,1 in which the material- I which will detonate onignition is a gaseous material.

References Cited file ot-this patent UNITED STATES PATENTS 961,350 7 V1,639,584 Bone Aug. 16, 1921? 2,690,960 Kistiakowsky et al. .OCt.fT5,1954" 2,832,665 Hertzberg et a1. Apr. 29, 1958 I FOREIGN PATENTS :ffi.26,728 Great Britain AD. 1905 OTHER REFERENCES" Lessing: ScientificAmerican, No. 5, vol. 1 88, pages v 29 to 35, May 1953.

' Hausser June1 4,1 91(

1. A PROCESS FOR THE PRODUCTION OF NITROGEN OXIDES WHICH COMPRISESCONFINING IN ONE PORTION OF A REACTION SPACE A MAKE CHARGE OF A GASEOUSMIXTURE CONSISTING ESSENTIALLY OF NITROGEN AND OXYGEEN, CONFINING INANOTHER PORTION OF TTHE REACTION SPACE A DETONATION CHARGE OF A MATERIALWHICH WILL DETONATE UPON IGNITION, IGNITING THE DETONATION CHARGE,IMPINGING THE RESULTING DETONATION WAVE AGAINST THE MAKE CHARGE WHEREBYTHE NITROGEN AND OXYGEEN OF THE MAKE CHARGE ARE CAUSED TO REACT.